In-Flight Mag Checks

RyanB

RyanB

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After reading Mike Busch’s article ‘The Mag Check’ (https://resources.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2010-12_the-mag-check.pdf) I’ve been routinely performing an in-flight check, which is something I’ve never done, until I came across this article. Definitely seems like a beneficial way to keep an eye on your ignition system and often times doesn’t seem to get discussed very much.

So, does anyone else do in-flight mag checks on a regular basis?
 
If you're running an EMS with EGT/CHT for each cylinder, and especially if you're planning on running LOP, why not give it a try. Its another tool in the box.
 
RyanB said:
After reading Mike Busch’s article ‘The Mag Check’ (https://resources.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2010-12_the-mag-check.pdf) I’ve been routinely performing an in-flight check, which is something I’ve never done, until I came across this article. Definitely seems like a beneficial way to keep an eye on your ignition system and often times doesn’t seem to get discussed very much.

So, does anyone else do in-flight mag checks on a regular basis?
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So I the run up was normal and a given power setting at altitude in my well maintained aircraft producing the published KTAS. Why do I need to do this mag check?
 
Yes, I do. I try to do it as I start my descent. Checked mine today leaving FL180. The reason to do it is because a weakness in the mag, wire harness or spark plug will show under these much harsher conditions may not at the quite low power and low altitude of a ground check. It just takes a minute to do. I think it would only be helpful if you have a full engine monitor and can watch what happens to all the EGTs.
 
Wouldn't you want to know if you had something weak in your ignition system? Wouldn't you want to learn that under controlled (by you) circumstances at altitude rather than on a dark and stormy night on an instrument approach at 600' in the clag? Wouldn't you want to know it going into your home field where you can get it fixed at normal pricing rather than at some Timbuktu airport with no maintenance? Wow. An inflight mag check, especially LOP, will show ignition weaknesses that will not be caught on a ground check. And ignition weaknesses do not get better. Finding it early can save a lot of time, expense and grief. If you've never done this and are "concerned," then fly with someone who does this as a normal course of business and see how uneventful it is.
 
I do ignition tests on run-up before departure and after landing.
 
Have always been afraid of a loud 'bang' when switching both mags back on.
Irrational? Maybe.
I think I'd be more comfortable at trying this with reduced power vs cruise, first.
And, briefly not 5 seconds.
 
Let'sgoflying! said:
Have always been afraid of a loud 'bang' when switching both mags back on.
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That won’t happen if it’s done correctly. You’re just switching from BOTH to L and R, just like you’d do during your run-up. If you inadvertently switched the key to OFF and then back on, than you’d definitely get a nasty backfire.
 
You can safely switch to L or R and back to Both. Don't go to Off. If you do, close the throttle before turning the mags back on, then open the throttle. Or pull the mixture to ICO and turn the mags on. Do the same if you find a mag dead.

The only risk here is having the switch fall apart as you check the mags. How often has that happened? And if it falls apart it should still run. It does require the switch parts to short the mags, and if they fall out they're not about to do that.

Someday you might have a rogue mag that starts sending sparks to the wrong places, causing massive power loss and frightening vibration and noises. What are you going to do if you're afraid of trying the switch to see if it improves anything? Crash?

A lot of pilots don't know what's going on up front, only that noise and wind come from it. They're afraid of the unknown.
 
RyanB said:
That won’t happen if it’s done correctly. You’re just switching from BOTH to L and R, just like you’d do during your run-up. If you inadvertently switched the key to OFF and then back on, than you’d definitely get a nasty backfire.
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Unless the one you switched off was the only one that was working...
 
I DEFINITELY wouldn't do this in a plane with a SureFly and a keyed ignition. Anyone who has one will know why.
 
I do, sometimes. I also do run-ups with lean mixture, full rich mixture run up does not show you anything that might be wrong with the mags itself. At best it will show you a bad plug.

Do it if you are an engine monitor and you can run the engine at leaner side of things and low power. When I do this, I make sure these is a landable area under me
 
I do it if I suspect something wrong or am doing a test flight. I haven't made it a routine procedure I perform every flight but wouldn't be opposed to it.
 
Another quick worthwhile mag test would be at idle (on the ground). The idle won't be smooth if the points are bad or any other marginal components.
 
That won’t happen if it’s done correctly. You’re just switching from BOTH to L and R, just like you’d do during your run-up. If you inadvertently switched the key to OFF and then back on, than you’d definitely get a nasty backfire.
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We are trained (and there is strong instinct) to immediately reverse the last switch we flipped, when there suddenly occurs a problem & is closely related chronologically to switch flipping.

So you turn off a mag and find the engine quits - what are most pilots going to do?
Yep, instantly flip that switch back on.

If you are carrying significant power, I believe you might cause some damage in some engines.
Few of us are mentally prepared to bring the throttle back before switching back on.
 
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N1120A said:
I DEFINITELY wouldn't do this in a plane with a SureFly and a keyed ignition. Anyone who has one will know why.
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Why would this be? How could they get the SureFly certified if there wasn't a smooth transition if either the SureFly or standard mag quit? What would happen with an inflight mag check shouldn't be any different than if either quit for real. Or at least I wouldn't think so.
 
Yeah, these kind of statements. :rolleyes:

I have a SureFly mag and I have no idea why you wouldn't do this.
 
RyanB said:
That won’t happen if it’s done correctly. You’re just switching from BOTH to L and R, just like you’d do during your run-up. If you inadvertently switched the key to OFF and then back on, than you’d definitely get a nasty backfire.
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Maybe not. If your in-flight mag check is done to diagnose a lack of performance caused by a dead mag (which in this hypothetical case occurred in flight) the nasty AFTERFIRE could destroy your muffler.

-Skip
 
Definitely a BAD IDEA! Mag checks are performed on the ground for a reason. They identify a potential problem BEFORE that problem could cause an issue in the air. The only reason one would have to do something like this in the air would be in diagnosing a problem that popped up during flight. However, if that problem in engine performance was enough to make you hunt for an issue, your time would be better spent in searching for the nearest available airport to land. Nothing about checking the mag in the air would make a problem any better so what benefit could there possibly be in doing something like this? There are MANY downsides to doing an in-flight mag check and no upsides that I can think of.
 
I can't think of a good-enough reason to be doing a mag check off the ground short of troubleshooting an engine problem. However, even then I'd not be inclined to mess with the mags unless I had a good reason to suspect it. Seems like very little upside for this "check".
 
donjohnston said:
Yeah, these kind of statements. :rolleyes:

I have a SureFly mag and I have no idea why you wouldn't do this.
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Do you have a rotary ignition switch? Or do you have mag toggle switches?

With a rotary key switch, the idea is that if the Surefly is on the right mag position, when you go from BOTH to R, you cross over L so there's a brief period of time that the Surefly is powered off. Depending on how quick you are with the key switch and what firmware version you are running, the reboot time on the Surefly could allow for a couple cycles of unburned fuel and then BANG.

Toggle switches on the mags eliminates this problem.
 
Kevin Eggert said:
Definitely a BAD IDEA! Mag checks are performed on the ground for a reason. They identify a potential problem BEFORE that problem could cause an issue in the air. The only reason one would have to do something like this in the air would be in diagnosing a problem that popped up during flight. However, if that problem in engine performance was enough to make you hunt for an issue, your time would be better spent in searching for the nearest available airport to land. Nothing about checking the mag in the air would make a problem any better so what benefit could there possibly be in doing something like this? There are MANY downsides to doing an in-flight mag check and no upsides that I can think of.
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And when you have a mag slip its distributor gearing and it starts firing at really bad times and causes massive roughness and power loss, you'll spend valuable time and altitude looking for a runway and neglect the troubleshooting that could save your life.

I am a Canadian aircraft maintenance engineer. I was a flight instructor. I taught Aircraft Systems in a college. It never ceases to amaze me how some pilots can presume to teach stuff they know so little about.
 
Kevin Eggert said:
Definitely a BAD IDEA! Mag checks are performed on the ground for a reason. They identify a potential problem BEFORE that problem could cause an issue in the air. The only reason one would have to do something like this in the air would be in diagnosing a problem that popped up during flight. However, if that problem in engine performance was enough to make you hunt for an issue, your time would be better spent in searching for the nearest available airport to land. Nothing about checking the mag in the air would make a problem any better so what benefit could there possibly be in doing something like this? There are MANY downsides to doing an in-flight mag check and no upsides that I can think of.
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not true. the typical mag checks that we are taught and even there in the POH, doesnt show anything other than fouled plugs or may be a dead mag. the only downside of this mag check in the air is if you switch to a bad mag and the sound stops and you switch back to both without closing the throttle or the mixture knob. i wonder how many people have closed the mixture in the air or turned the ignition to off position ...ever
 
I think there is "message creep" here. The OP suggested routine in flight mag testing, which is what most of the responses are focused on, versus checking a bad running engine.

If there is an engine problem, my training was 1) establish max glide, 2) look for place to land, and then 3) trouble shoot. These are the priorities which will have a higher chance of saving your life. And with this scenario, Dan's suggestion of doing an in flight mag check sounds good. I was taught to trouble shoot by switching tanks, putting on full mix, turning on carb heat, then checking mags. If it works, great. If not, you're set up for landing someplace.

But should the mags be tested in flight with a good running engine? Is the potential benefit worth the potential problem caused by the test? What is the probability of finding a mag problem that didn't pop up on the ground? My practice is not to do that, as I'm on the side of the juice isn't worth the squeeze, and I might cause more harm than the good I might do.
 
Everskyward said:
Unless the one you switched off was the only one that was working
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this would be my concern. Had a dead mag once and the engine ran fine on it, you could only tell the mag was dead by the engine actually shutting off when it was switched over to it. Something I'd rather not experiment with in the air

WannFly said:
I also do run-ups with lean mixture
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This was something that was showed to me wayyyy too late in my aviation life. And it makes total sense. A very lean mag check is far more "sensitive" to mag issues and has the added benefit of clearing up any plug fouling while still on the ground

I'm not saying a mag check in the air is necessarily bad, but it's something I would do sparingly and be wise about what I'm over when I start messing with my engine's ignition system
 
I had a bad wiring harness lead to one plug. The ground mag check where the load on the ignition system is pretty much at its minimum did not show it. The inflight mag check clearly did and with the engine monitor I easily identified the plug that wasn't firing. Because I "believed" the ground check as many of you apparently do, I had to see this in the air a couple of times before I knew I had a problem to trouble shoot, and the inflight mag check made it easy to do so. So my vote based on actual personal experience is to do an inflight mag check every flight and know my whole ignition system is working as it should.
 
Tantalum said:
This was something that was showed to me wayyyy too late in my aviation life. And it makes total sense. A very lean mag check is far more "sensitive" to mag issues and has the added benefit of clearing up any plug fouling while still on the ground
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same here. in my PPL i was taught by the POH and mostly to leave the red knob alone. for in flight mag check check i agree and i only do it sometimes, during test flights. if I am going somewhere, my philosophy is if the fan is working up front, dont mess with it
 
Lance F said:
I had a bad wiring harness lead to one plug. The ground mag check where the load on the ignition system is pretty much at its minimum did not show it. The inflight mag check clearly did and with the engine monitor I easily identified the plug that wasn't firing. Because I "believed" the ground check as many of you apparently do, I had to see this in the air a couple of times before I knew I had a problem to trouble shoot, and the inflight mag check made it easy to do so. So my vote based on actual personal experience is to do an inflight mag check every flight and know my whole ignition system is working as it should.
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when you did the mag check on the ground, if you put your engine monitor on NRM mode, it should catch the bad plug/ the plug not firing - or so I have been told. curious to know if you found that to be true?
 
WDD said:
I think there is "message creep" here. The OP suggested routine in flight mag testing, which is what most of the responses are focused on, versus checking a bad running engine.

If there is an engine problem, my training was 1) establish max glide, 2) look for place to land, and then 3) trouble shoot. These are the priorities which will have a higher chance of saving your life. And with this scenario, Dan's suggestion of doing an in flight mag check sounds good. I was taught to trouble shoot by switching tanks, putting on full mix, turning on carb heat, then checking mags. If it works, great. If not, you're set up for landing someplace.

But should the mags be tested in flight with a good running engine? Is the potential benefit worth the potential problem caused by the test? What is the probability of finding a mag problem that didn't pop up on the ground? My practice is not to do that, as I'm on the side of the juice isn't worth the squeeze, and I might cause more harm than the good I might do.
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My point is that if you're scared to touch that switch in flight, you're not likely to try it if the engine starts acting up.

We get carb ice accidents because pilots pull the carb heat and the engine runs worse, so they push the knob back in. So the ice continues to build and kills the engine and the airplane crashes for no good reason. We get fouled sparkplugs and terrible fuel mileage because some folks are scared to touch that mixture knob because the engine might quit if they pull it out too far and maybe it won't start again or something. We get people who learned to fly in 172s that are scared to move the fuel selector off of Both. It's silly. IMHO it's too easy to get a PPL, and the accident stats show it.
 
Sorry to hear that is what you see. FWIW I was taught to move all of those leavers, leave carb heat on until it clears, adjust the mix, and check the mags if in flight engine malfunction.
 
WannFly said:
when you did the mag check on the ground, if you put your engine monitor on NRM mode, it should catch the bad plug/ the plug not firing - or so I have been told. curious to know if you found that to be true?
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I do the ground check in NRM mode and look for the egt rise on each cylinder. (I don't really even look at the rpm drop.) In the case I'm citing the plug did fire during the ground check on multiple occasions. With the higher demand under power at altitude something in the lead was not adequate to fire the plug. The in flight check showed the cylinder egt drop off when the mag with the bad lead was the one that was on.

Since we have some thread drift going on here anyway, I will say that I think it's a CFI failure that so many pilots are unwilling to do in flight mag checks, and unwilling to lean properly on every flight, and unwilling to use the carb heat long enough to do some good, and unwilling to use all the fuel in an aux tank, and unwilling to at least understand and consider LOP operations, and so much more. All I can say is that because of this so many pilots are not getting full, safe utilization of the planes they are flying. Rant off.
 
Lance F said:
I do the ground check in NRM mode and look for the egt rise on each cylinder. (I don't really even look at the rpm drop.) In the case I'm citing the plug did fire during the ground check on multiple occasions. With the higher demand under power at altitude something in the lead was not adequate to fire the plug. The in flight check showed the cylinder egt drop off when the mag with the bad lead was the one that was on.
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interesting. thanks for sharing
 
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